The response of platelets to stimuli will be studied to determine what mechanisms couple specific stimuli to the varide responses and the sequence of events involved. Emphasis will be on secretion, aggregation and shape change (morphological responses) and activation of phosphorylase (a metabolic response). Time courses for these responses will be compared and drugs will be used to modify the responses. The role of calcium will be investigated using drugs (such as local anaesthetics) that affect calcium metabolism in order to identify calcium compartments. The type of metabolic conversion of phosphorylase will be studied by separating the active species and studying their interconversion.